[ChrisA]

It does not make a great difference as to what is touching the rubber. Whether that is conductive or not makes no difference. When the rubber of the wheel rubs against the HDPE the HDPE is given a charge. When a material that is at a different potential than that of the HDPE the electrons will naturally want to jump from one to the other to even it out which causes an arc. This is the static that is being seen and felt from the HDPE.

I would have thought everyone would have figured this out by now, but I guess that this is not the case.